In a yam feeding device which is known from WO 91/14032, a brake disc which defines the counter-brake surface of an output brake on the storage drum is tilted by means of a tilting element relative to the brake element, which abuts thereon with the brake surface, so as to open a wedge-shaped gap for threading a yam. The tilting element which is stored in the storage drum is operated by a piston rod of a piston which is displaceable in the pressure chamber of a mounting. The pressure chamber is connectable to a source of pressure by which a threading nozzle arranged in the output brake is also supplied. Apart from the great constructional efforts required for the brake opening device, it is difficult under adverse conditions to thread the yam properly into and through the output brake.
In a yam feeding device which is known from EP 0 567 045 A1, a piston rod which is extensible by means of a piston is provided outside of and next to the surface of the storage drum, with the piston rod directly acting on a brake surface-defining brake band of the brake element or on the brake element, and lifting the brake band in a locally defined area from the counter-brake surface on the storage drum to open a crescent-shaped threading gap for the yam. Apart from the constructional efforts and the problem of accommodating such an apparatus in view of the normally very limited space, the mechanical load on the brake element and the brake surface is great.
U.S. Pat. No. 5 778 943 (Tholander) discloses a remotely controlled output brake of a yarn feeder, namely an output brake, the brake element of which can be switched between on/off breaking conditions. In the on condition, the brake element is pressed axially against a counter-surface of the feeder storage body with a contact force set by the axial position of the sleigh positioning the entire brake arrangement at the front end region of the storage body. In the off position, said brake element contacts the counter-surface with almost no axial contact pressure or even is slightly detached therefrom. The actuation mechanism, e.g. a pneumatic drive, is integrated into the carrier structure of the brake arrangement. Said actuating mechanism engages in an outer holding ring of the brake element or via a push collar at a deformable portion of said brake element.
However, said actuation mechanism is not intended to provide a threading position of the brake element with sufficient axial distance between the brake element and the counter-surface to thread in a new yarn. Threading requires that the entire brake arrangement be displaced via its sleigh along the adjustment screw. Said procedure is time-consuming and cumbersome and nullifies the set contact pressure adjustment.
It is the object of the present invention to provide a yarn feeding device of the above-mentioned type and a method of opening an output brake which enable a yam of any desired yam quality to be threaded into and through the output brake rapidly and without any problems and at any time.
According to the invention, a brake opening device is provided for opening the brake with a sufficient stroke to allow the threading of a new yarn. Said brake opening device has an axially movable boundary wall which is pneumatically loadable in order to move with the pneumatic pressure in an axial direction. Said boundary wall is connected in motion transmitting fashion to said brake element in order to move said brake element with its brake surface into an axial position where said brake surface is sufficiently lifted from said counter brake surface to allow a new yarn to be passed therebetween.
In the embodiment wherein the boundary wall is pressurized by an elevated pressure or a vacuum to move the brake element to a threading position, the threading-in position can rapidly be established under small constructional efforts with the brake surface being entirely lifted from the counter-brake surface. The yam passes in unhindered fashion into the output brake, and it is above all easy to thread the yam through the output brake because it is nowhere clamped between the brake surface arid the counter-brake surface during the clock hand-like rotational movement along the free end of the storage drum. The brake opening device manages with a small number of components, it is space-saving and does not impair the normal brake function of the output brake.
Where a threading nozzle creates a suction flow acting on the pressure chamber adjacent the boundary wall the threading nozzle which is provided for automatically threading the yam feeding device is also used for adjusting the brake element into the threading position. When the boundary wall is moved under excess pressure, the pressure chamber can be connected to the same compressed-air supply as the threading nozzle. By contrast, when the boundary wall is acted upon with vacuum, the suction pressure of the suction flow of the threading nozzle is expediently used. Both measures have the benefit that upon start of a threading operation in the yam feeding device the brake element is automatically brought into the threading position and is already in the threading position when the free yam end arrives at the output brake.
However, it is also possible to connect the pressure chamber to a separate source of excess pressure or vacuum and to bring the brake element at a suitable time, for instance in advance of the activation of the threading nozzle, into the threading position.
The embodiment wherein the boundary wall is an elastic circular ring membrane is constructionally simple and reliable in function. An elastomer or rubber is suited as the material for the circular ring membrane. The circular ring membrane has the important advantage that it closes the interior of the mounting of the brake element to the outside, so that no impurities or lint pass into the output brake. The circular ring membrane can, for instance, be fixed by using an adhesive on the inner edge region and the outer edge region. However, it is also possible to fix the circular ring membrane by screwing or clamping. A planar circular ring membrane is here expediently used. However, it is also possible to use a membrane formed with concentric undulations to impair the intrinsic mobility of the brake element during the braking function as little as possible.
Alternatively, the embodiment is expedient, in which a circular ring piston is used for adjusting the brake element into the threading position. It is here possible to arrange the circular ring piston separated from the brake element and only to couple it with the brake element for moving said element into the threading position, for example, by the measures that the circular ring piston which is held by a restoring spring in an initial position acts on a carrier of the brake element upon actuation following an initial empty stroke and carries said element along. During normal braking function, the intrinsic mobility of the brake element which is important for the operation of the output brake is not at all impaired.
The embodiment wherein the circular ring piston is provided on the brake element or a tubular attachment connected thereto is advantageous because a simple adjustment of the brake element into the threading position is made possible with a few components.
Alternatively, the embodiment wherein the boundary wall is an end of a circular, hollow spring bellows is of importance, in which the spring bellows fulfills a double function because for threading purposes it is responsible for the adjustment of the brake element into the threading position, whereas otherwise it produces a resilient clamping of the brake surface against the counter-brake surface. The spring bellows may be made of metal or plastics.
Another important embodiment is provided wherein the brake element is a frustoconical jacket having a large opening which fits over a free end of the storage drum. This is an output brake of a very modem type in which the brake element cooperates by means of a wear-resistant brake band with the withdrawal edge region of the storage drum, i.e. on a relatively large diameter. Despite the relatively high spring force by which the jacket is axially pressed against the storage drum end, the brake element of this brake type can be rapidly and reliably adjusted with the boundary wall into the threading position in which the brake surface is lifted expediently completely from the counter-brake surface, so that the yam can be threaded through very easily. Mechanical load or deformation on the brake band is not at all observed here.
An alternative embodiment is an axial disc brake in which the yam enters from the outside and is deflected in the center of the brake element in withdrawal direction. The output brake operates on a relatively small diameter in comparison with the outer diameter of the storage drum, which permits a very sensitive braking operation and a brake element with a rapid response because of its light-weight construction. The brake element is rapidly moved by the boundary wall into the threading position in which the brake surface is lifted expediently completely from the counter-brake surface. The circular ring membrane protects the interior of the output brake against dirt and lint.
In the embodiment wherein the opposing brake surfaces are arranged in a direction perpendicular to an axial direction of the storage drum the brake surface and the counter-brake surface are substantially in a direction perpendicular to the axial drum direction. The yam which arrives in an inclined manner is first deflected radially to the interior and is then again deflected from the radial direction into the withdrawal direction. It is gently braked between the surfaces. The counter-brake surface can be arranged on a brake disc of its own, the brake disc being held on the storage drum, expediently movably. It is also possible to provide the counter-brake surface directly at the front ends of the storage drum. However, the brake surface and the counter-brake surface may also be conical to facilitate entry of the yam during threading.
In a further embodiment, the brake element is supported on a tubular attachment which is guided in a guide channel where such guide channel includes longitudinally extending ribs. This embodiment ensures a clean and easy guiding of the brake element and also a flow path with a large cross-section into and out of the pressure chamber.
Where the storage drum and brake element define, brake surfaces and the brake element is moved by suction pressure, the brake element can be lifted rapidly and expediently entirely from the brake surface to form a threading opening for the yam, the opening being open from all feed directions. The demand made on such output brakes because of the type of construction, according to which the brake element which is resiliently supported in the mounting under spring action towards the storage drum should be moved away from the storage drum in axial direction for threading the yam, can be met especially easily by the application of suction pressure.
According to claim 13 the suction pressure of the suction flow which is produced at any rate for threading the yam is used in an especially expedient manner for lifting the brake element from the brake surface, whereby a separate source of negative pressure can be dispensed with on the one hand and the opening movement of the output brake is synchronized, at least substantially, on the other hand by the simultaneously started threading process of the yam feeding device.